The cerebellum is a part of the hindbrain that plays a crucial role in the coordination of voluntary movements.
Its primary functions include maintaining muscle tone, regulating posture, and ensuring smooth and balanced muscular activity.
It does not directly control thinking — that is a function of the cerebral cortex.
Hearing is a function of the auditory pathways in the temporal lobe and the cochlea, not the cerebellum.
Reticular formation is a separate structure in the brainstem responsible for alertness and arousal, not a function of the cerebellum itself.
Therefore, the correct answer is muscle tone and posture.